Cationic micronutrients

Humic substances can form complexes with metals, including cationic micronutrients (36), thanks to the presence of electron-donor functional groups in these molecules. It therefore appears evident that due to these properties, humic substances can contribute to the regulation of the chemical balances of metals, thus influencing their solubility (5). With regard to plant availability, the molecular dimension and solubility of humic substances are very important. 

Polycarbonyl and polyamino compounds include chelates, which are manmade compounds, and siderophores, which are biologically derived and more specialized. They can help dissolve inorganic ions, keep ions in one specific ionic state, and maintain them in biologically available forms. Because of their ability to bring ions into solution, they are often used to extract specific ions in specific forms from soil. Cationic micronutrients, particularly iron and zinc, are often applied in chelated form as a foliar spray to alleviate nutrient deficiencies. This is particularly true of plants growing in basic soil and is done even when plants do not show micronutrient deficiencies. Typically, both foliar and soil applications are effective in this regard. 

M. Treeby, H. Marschner, and V. Rdmheld, Mobilization of iron and other micronutrient cations from a calcareous soil by plant-borne, microbial, and synthetic metal chelators. Plant Soil II4 2 1 (1989). 

Hodgson J.F., Lindsay W.L., Trierweiler J.F. Micronutrient cation complexing in soil solution. II. Complexing of zinc and copper in displaced solution from calcareous soils. Soil Sci Soc A Proc 1966 30 723-726. 

The structures show the lone pairs of electrons that form bonds with metal cations. Both chelates and siderophores hold micronutrient cations in solution and in a biologically available form until the cations can be used by the... 

Figure 3.6. Modes of interaction of natural organic matter with a clay mineral surface. The figure depicts cation (M) and water bridging, along with van der Waals interactions (through the sugar moiety). Reprinted with permission from Stevenson, F. J., and Ardakani, M. S. (1972). Organic matter reactions involving micronutrients in soils. In Micronutrients in Agriculture, Mortvedt, J. J., Giordano, P. M., and Lindsay, W. L., eds., Soil Science Society of America, Madison, WI, pp. 79-114.

At Chevron and elsewhere a whole series of copper, zinc, manganese, calcium, cadmium, lead and arsenic salts were manufactured as plant protection agents and micronutrients by the carefully pH controlled precipitation of insolubles where the active cation or anion could only reach a small, plant-tolerable, maximum concentration. In such cases this maximum could be calculated... 

Geering, H. R., Hodgson, J. F., and Sdano, C. Micronutrient cation complexes in soil solution IV. The chemical state of manganese in soil solution. Soil Sci. Soc. Am. Proc. 33 81-85 (1969). 

The supply of the coppice will be undertaken by Yorkshire Environmental Ltd., which will try to maximise the utilisation of biomass fuels supplied by short rotation forestry. Slurry of domestic treated sewage sludge supplied by Yorkshire Wafer Services Ltd. will be applied to the coppice plantations as organic fertiliser to increase crop yield. The sludge will be low in heavy metal, pathogens and odour. Waste ash from both the gasifier and the catalytic cracker will be recycled to the coppice plantations as a soil conditioner and source of base cations and micronutrients to improve soil fertility. 

Natural waters from all sources, including soils, lakes, streams, estuaries, and the ocean (see review of Stevenson, 1983) have been found to contain trace metals in organically bound forms. The micronutrient cations in displaced soil solutions have also been shown to occur partly in organically bound forms (Geering et al., 1969). Trace metals that would ordinarily convert to insoluble precipitates (as carbonates, sulfides, or hydroxides) at the pH values found in many soils, sediments, and natural waters are undoubt-... 

Chelation by LMMO substances is a major factor in the transport of micronutrient cations such as Cu, Zn, Ni, Fe, and Mn to root surface by mass flow and diffusion. In soil solutions of calcareous soils 40 to 75% of tlie zinc and 98% of copper have been found in organic complexes (Hodgson et al., 1966 Sanders, 1982, 1983 McGrath et al., 1988). For plants the importance of complexed micronutrients in the soil solution is particularly evident in calcareous soils. This is also indicated by the fact that soil extractions with synthetic chelators such as EDTA and DTPA provide suitable soil tests for estimation of available micronutrieiits (Sims and Johnson, 1991) (summarized in detail in Section 11.3). 

The transition and heavy metals, referred to hereafter as trace metals, are important to plants and animals as both micronutrients and toxic elements. Many of them occur in the soil environment in cation form. As naturally occurring elements, some of these cations are incorporated into primary and secondary mineral structures and may be very unavailable. Schemes for complete extraction of these metals from soils require extreme treatments, including dissolution of certain minerals. As pollutants, the metals may enter the soil in organically complexed form or as metal salts. In the latter case, the metal cations then adsorb on mineral and organic surfaces. 

The micronutrient cations can be estimated in a single extraction with diethylene triamine pentaacetic acid (DTPA) which has excellent chelating property with the micronutrient elements. Adequate precaution must be taken against any likely contamination from the reagents and glass wares in micronutrient assay work. Only double distilled water should be used. Specific hallow cathode lamps for each elements are used on AAS and requisite standards for instrument calibration are prepared as per instructions in the operation manual. 

Estimate the micronutrient cations (Zn +, Cu +, Fe +, Mn +) with the help of atomic absorption spectrophotometer. 

Description. Potassium is an essential mineral micronutrient in human nutrition it is the major cation inside animal cells, and it is thus important in maintaining fluid and electrolyte balance in the body. Potassium is also important in allowing muscle contraction and the sending of all nerve impulses in animals. 

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